Cooling lubrication in the engagement zone of tools belongs to the state of the art in technology. Previously known processes require substantial volumes of liquid, e.g. ranging from 10 to 1,000 l/min per tool. In the process the cooling lubricant is supplied from outside at for example 5 bar pressure to the point of engagement of the cutting edge.
The state of the art in technology also comprises methods according to which the cooling lubrication of the tool is accomplished from outside, utilizing small amounts of liquid by exploiting compressed-air spraying devices.
Previously known are also methods according to which the feed is effected to the cutting edge point of engagement through the working spindle and through the tool itself. Pressure rates of up to 100 bar are common practice in these methods.
Known from DE 42 00 808 Al is a working unit comprised of a driven rotating spindle where a chucking device for a drilling or milling tool is mounted at the spindle and where the spindle and the drilling or milling tool each are equipped with a central bore and where the drilling or milling tool are provided with an outlet port for feed of the lubricant or coolant to the cutting zone. The bores in this method are supplied with compressed air while the lubricant is fed through a separate thin pipe laid through the bores up into the interior of the tool end. The devices for varying and disrupting the feed of lubricant and coolant are located outside the cutting unit. This method only allows for a sluggish and time-retarded variation of the lubricant and coolant feed in the cutting zone.
DE 38 17 799 Cl moreover describes a rotary passage for fluids, particularly for machine tool spindles, where, at the transition from a stationary casing to a pivoted hollow shaft, springloaded barrier valves are arranged which allow for shutting-off the flow-through ducts for air and liquid. Air and the cooling lubricant here are mixed downstream of the barrier valves in a hollow shaft and supplied through a feeder duct to the cutting zone. To allow for what is called dry machining it is also provided for that only air will be blown through the hollow shaft and the feeder duct into the tool take-up when tools are changed.
The problem of dosing systems of this type for dry machining is that the coolant feed to the cutting zone cannot be interrupted quickly enough for tools change and not without post-running and that after a tools change a sufficient amount of cooling lubricant will be available in the cutting zone with a substantial delay only. In case of high spindle speeds it also involves the problem that the liquid medium is sluiced out from the current of air due to the centrifugal force and will deposit at the walls of the hollow shaft. It is above all this precipitation at the tube walls that causes a substantial delay in the supply of liquid to the cutting zone after tools change because it takes some time until the liquid has "crept" along tube walls to the tool. In case of extensions in the cross section it is moreover necessary to fill the expanded cavities with cooling lubricant before it reaches the tool. The dosage of the cooling lubricant air mixture at the tool is thus very unprecise and sluggish when known devices are implemented.